lib-storage: Fixed deleting mailbox when mail_attribute_dict wasn't set.
lib-storage: Fixed deleting mailbox when mail_attribute_dict wasn't set.

LTD-Beget/dovecot,LTD-Beget/dovecot,LTD-Beget/dovecot,LTD-Beget/dovecot,LTD-Beget/dovecot